1 //=== StdLibraryFunctionsChecker.cpp - Model standard functions -*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This checker improves modeling of a few simple library functions. 10 // 11 // This checker provides a specification format - `Summary' - and 12 // contains descriptions of some library functions in this format. Each 13 // specification contains a list of branches for splitting the program state 14 // upon call, and range constraints on argument and return-value symbols that 15 // are satisfied on each branch. This spec can be expanded to include more 16 // items, like external effects of the function. 17 // 18 // The main difference between this approach and the body farms technique is 19 // in more explicit control over how many branches are produced. For example, 20 // consider standard C function `ispunct(int x)', which returns a non-zero value 21 // iff `x' is a punctuation character, that is, when `x' is in range 22 // ['!', '/'] [':', '@'] U ['[', '\`'] U ['{', '~']. 23 // `Summary' provides only two branches for this function. However, 24 // any attempt to describe this range with if-statements in the body farm 25 // would result in many more branches. Because each branch needs to be analyzed 26 // independently, this significantly reduces performance. Additionally, 27 // once we consider a branch on which `x' is in range, say, ['!', '/'], 28 // we assume that such branch is an important separate path through the program, 29 // which may lead to false positives because considering this particular path 30 // was not consciously intended, and therefore it might have been unreachable. 31 // 32 // This checker uses eval::Call for modeling pure functions (functions without 33 // side effets), for which their `Summary' is a precise model. This avoids 34 // unnecessary invalidation passes. Conflicts with other checkers are unlikely 35 // because if the function has no other effects, other checkers would probably 36 // never want to improve upon the modeling done by this checker. 37 // 38 // Non-pure functions, for which only partial improvement over the default 39 // behavior is expected, are modeled via check::PostCall, non-intrusively. 40 // 41 // The following standard C functions are currently supported: 42 // 43 // fgetc getline isdigit isupper 44 // fread isalnum isgraph isxdigit 45 // fwrite isalpha islower read 46 // getc isascii isprint write 47 // getchar isblank ispunct 48 // getdelim iscntrl isspace 49 // 50 //===----------------------------------------------------------------------===// 51 52 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 53 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 54 #include "clang/StaticAnalyzer/Core/Checker.h" 55 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 56 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h" 57 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 58 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.h" 59 60 using namespace clang; 61 using namespace clang::ento; 62 63 namespace { 64 class StdLibraryFunctionsChecker 65 : public Checker<check::PreCall, check::PostCall, eval::Call> { 66 /// Below is a series of typedefs necessary to define function specs. 67 /// We avoid nesting types here because each additional qualifier 68 /// would need to be repeated in every function spec. 69 struct Summary; 70 71 /// Specify how much the analyzer engine should entrust modeling this function 72 /// to us. If he doesn't, he performs additional invalidations. 73 enum InvalidationKind { NoEvalCall, EvalCallAsPure }; 74 75 // The universal integral type to use in value range descriptions. 76 // Unsigned to make sure overflows are well-defined. 77 typedef uint64_t RangeInt; 78 79 /// Normally, describes a single range constraint, eg. {{0, 1}, {3, 4}} is 80 /// a non-negative integer, which less than 5 and not equal to 2. For 81 /// `ComparesToArgument', holds information about how exactly to compare to 82 /// the argument. 83 typedef std::vector<std::pair<RangeInt, RangeInt>> IntRangeVector; 84 85 /// A reference to an argument or return value by its number. 86 /// ArgNo in CallExpr and CallEvent is defined as Unsigned, but 87 /// obviously uint32_t should be enough for all practical purposes. 88 typedef uint32_t ArgNo; 89 static const ArgNo Ret; 90 91 class ValueConstraint; 92 93 // Pointer to the ValueConstraint. We need a copyable, polymorphic and 94 // default initialize able type (vector needs that). A raw pointer was good, 95 // however, we cannot default initialize that. unique_ptr makes the Summary 96 // class non-copyable, therefore not an option. Releasing the copyability 97 // requirement would render the initialization of the Summary map infeasible. 98 using ValueConstraintPtr = std::shared_ptr<ValueConstraint>; 99 100 /// Polymorphic base class that represents a constraint on a given argument 101 /// (or return value) of a function. Derived classes implement different kind 102 /// of constraints, e.g range constraints or correlation between two 103 /// arguments. 104 class ValueConstraint { 105 public: 106 ValueConstraint(ArgNo ArgN) : ArgN(ArgN) {} 107 virtual ~ValueConstraint() {} 108 /// Apply the effects of the constraint on the given program state. If null 109 /// is returned then the constraint is not feasible. 110 virtual ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 111 const Summary &Summary) const = 0; 112 virtual ValueConstraintPtr negate() const { 113 llvm_unreachable("Not implemented"); 114 }; 115 ArgNo getArgNo() const { return ArgN; } 116 117 protected: 118 ArgNo ArgN; // Argument to which we apply the constraint. 119 }; 120 121 /// Given a range, should the argument stay inside or outside this range? 122 enum RangeKind { OutOfRange, WithinRange }; 123 124 /// Encapsulates a single range on a single symbol within a branch. 125 class RangeConstraint : public ValueConstraint { 126 RangeKind Kind; // Kind of range definition. 127 IntRangeVector Args; // Polymorphic arguments. 128 129 public: 130 RangeConstraint(ArgNo ArgN, RangeKind Kind, const IntRangeVector &Args) 131 : ValueConstraint(ArgN), Kind(Kind), Args(Args) {} 132 133 const IntRangeVector &getRanges() const { 134 return Args; 135 } 136 137 private: 138 ProgramStateRef applyAsOutOfRange(ProgramStateRef State, 139 const CallEvent &Call, 140 const Summary &Summary) const; 141 ProgramStateRef applyAsWithinRange(ProgramStateRef State, 142 const CallEvent &Call, 143 const Summary &Summary) const; 144 public: 145 ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 146 const Summary &Summary) const override { 147 switch (Kind) { 148 case OutOfRange: 149 return applyAsOutOfRange(State, Call, Summary); 150 case WithinRange: 151 return applyAsWithinRange(State, Call, Summary); 152 } 153 llvm_unreachable("Unknown range kind!"); 154 } 155 156 ValueConstraintPtr negate() const override { 157 RangeConstraint Tmp(*this); 158 switch (Kind) { 159 case OutOfRange: 160 Tmp.Kind = WithinRange; 161 break; 162 case WithinRange: 163 Tmp.Kind = OutOfRange; 164 break; 165 default: 166 llvm_unreachable("Unknown RangeConstraint kind!"); 167 } 168 return std::make_shared<RangeConstraint>(Tmp); 169 } 170 }; 171 172 class ComparisonConstraint : public ValueConstraint { 173 BinaryOperator::Opcode Opcode; 174 ArgNo OtherArgN; 175 176 public: 177 ComparisonConstraint(ArgNo ArgN, BinaryOperator::Opcode Opcode, 178 ArgNo OtherArgN) 179 : ValueConstraint(ArgN), Opcode(Opcode), OtherArgN(OtherArgN) {} 180 ArgNo getOtherArgNo() const { return OtherArgN; } 181 BinaryOperator::Opcode getOpcode() const { return Opcode; } 182 ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 183 const Summary &Summary) const override; 184 }; 185 186 class NotNullConstraint : public ValueConstraint { 187 using ValueConstraint::ValueConstraint; 188 // This variable has a role when we negate the constraint. 189 bool CannotBeNull = true; 190 191 public: 192 ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 193 const Summary &Summary) const override { 194 SVal V = getArgSVal(Call, getArgNo()); 195 DefinedOrUnknownSVal L = V.castAs<DefinedOrUnknownSVal>(); 196 if (!L.getAs<Loc>()) 197 return State; 198 199 return State->assume(L, CannotBeNull); 200 } 201 202 ValueConstraintPtr negate() const override { 203 NotNullConstraint Tmp(*this); 204 Tmp.CannotBeNull = !this->CannotBeNull; 205 return std::make_shared<NotNullConstraint>(Tmp); 206 } 207 }; 208 209 /// The complete list of constraints that defines a single branch. 210 typedef std::vector<ValueConstraintPtr> ConstraintSet; 211 212 using ArgTypes = std::vector<QualType>; 213 using Cases = std::vector<ConstraintSet>; 214 215 /// Includes information about 216 /// * function prototype (which is necessary to 217 /// ensure we're modeling the right function and casting values properly), 218 /// * approach to invalidation, 219 /// * a list of branches - a list of list of ranges - 220 /// A branch represents a path in the exploded graph of a function (which 221 /// is a tree). So, a branch is a series of assumptions. In other words, 222 /// branches represent split states and additional assumptions on top of 223 /// the splitting assumption. 224 /// For example, consider the branches in `isalpha(x)` 225 /// Branch 1) 226 /// x is in range ['A', 'Z'] or in ['a', 'z'] 227 /// then the return value is not 0. (I.e. out-of-range [0, 0]) 228 /// Branch 2) 229 /// x is out-of-range ['A', 'Z'] and out-of-range ['a', 'z'] 230 /// then the return value is 0. 231 /// * a list of argument constraints, that must be true on every branch. 232 /// If these constraints are not satisfied that means a fatal error 233 /// usually resulting in undefined behaviour. 234 struct Summary { 235 const ArgTypes ArgTys; 236 const QualType RetTy; 237 const InvalidationKind InvalidationKd; 238 Cases CaseConstraints; 239 ConstraintSet ArgConstraints; 240 241 Summary(ArgTypes ArgTys, QualType RetTy, InvalidationKind InvalidationKd) 242 : ArgTys(ArgTys), RetTy(RetTy), InvalidationKd(InvalidationKd) {} 243 244 Summary &Case(ConstraintSet&& CS) { 245 CaseConstraints.push_back(std::move(CS)); 246 return *this; 247 } 248 Summary &ArgConstraint(ValueConstraintPtr VC) { 249 ArgConstraints.push_back(VC); 250 return *this; 251 } 252 253 private: 254 static void assertTypeSuitableForSummary(QualType T) { 255 assert(!T->isVoidType() && 256 "We should have had no significant void types in the spec"); 257 assert(T.isCanonical() && 258 "We should only have canonical types in the spec"); 259 } 260 261 public: 262 QualType getArgType(ArgNo ArgN) const { 263 QualType T = (ArgN == Ret) ? RetTy : ArgTys[ArgN]; 264 assertTypeSuitableForSummary(T); 265 return T; 266 } 267 268 /// Try our best to figure out if the call expression is the call of 269 /// *the* library function to which this specification applies. 270 bool matchesCall(const CallExpr *CE) const; 271 }; 272 273 // The same function (as in, function identifier) may have different 274 // summaries assigned to it, with different argument and return value types. 275 // We call these "variants" of the function. This can be useful for handling 276 // C++ function overloads, and also it can be used when the same function 277 // may have different definitions on different platforms. 278 typedef std::vector<Summary> Summaries; 279 280 // The map of all functions supported by the checker. It is initialized 281 // lazily, and it doesn't change after initialization. 282 mutable llvm::StringMap<Summaries> FunctionSummaryMap; 283 284 mutable std::unique_ptr<BugType> BT_InvalidArg; 285 286 // Auxiliary functions to support ArgNo within all structures 287 // in a unified manner. 288 static QualType getArgType(const Summary &Summary, ArgNo ArgN) { 289 return Summary.getArgType(ArgN); 290 } 291 static QualType getArgType(const CallEvent &Call, ArgNo ArgN) { 292 return ArgN == Ret ? Call.getResultType().getCanonicalType() 293 : Call.getArgExpr(ArgN)->getType().getCanonicalType(); 294 } 295 static QualType getArgType(const CallExpr *CE, ArgNo ArgN) { 296 return ArgN == Ret ? CE->getType().getCanonicalType() 297 : CE->getArg(ArgN)->getType().getCanonicalType(); 298 } 299 static SVal getArgSVal(const CallEvent &Call, ArgNo ArgN) { 300 return ArgN == Ret ? Call.getReturnValue() : Call.getArgSVal(ArgN); 301 } 302 303 public: 304 void checkPreCall(const CallEvent &Call, CheckerContext &C) const; 305 void checkPostCall(const CallEvent &Call, CheckerContext &C) const; 306 bool evalCall(const CallEvent &Call, CheckerContext &C) const; 307 308 enum CheckKind { CK_StdCLibraryFunctionArgsChecker, CK_NumCheckKinds }; 309 DefaultBool ChecksEnabled[CK_NumCheckKinds]; 310 CheckerNameRef CheckNames[CK_NumCheckKinds]; 311 312 private: 313 Optional<Summary> findFunctionSummary(const FunctionDecl *FD, 314 const CallExpr *CE, 315 CheckerContext &C) const; 316 Optional<Summary> findFunctionSummary(const CallEvent &Call, 317 CheckerContext &C) const; 318 319 void initFunctionSummaries(CheckerContext &C) const; 320 321 void reportBug(const CallEvent &Call, ExplodedNode *N, 322 CheckerContext &C) const { 323 if (!ChecksEnabled[CK_StdCLibraryFunctionArgsChecker]) 324 return; 325 // TODO Add detailed diagnostic. 326 StringRef Msg = "Function argument constraint is not satisfied"; 327 if (!BT_InvalidArg) 328 BT_InvalidArg = std::make_unique<BugType>( 329 CheckNames[CK_StdCLibraryFunctionArgsChecker], 330 "Unsatisfied argument constraints", categories::LogicError); 331 auto R = std::make_unique<PathSensitiveBugReport>(*BT_InvalidArg, Msg, N); 332 bugreporter::trackExpressionValue(N, Call.getArgExpr(0), *R); 333 C.emitReport(std::move(R)); 334 } 335 }; 336 337 const StdLibraryFunctionsChecker::ArgNo StdLibraryFunctionsChecker::Ret = 338 std::numeric_limits<ArgNo>::max(); 339 340 } // end of anonymous namespace 341 342 ProgramStateRef StdLibraryFunctionsChecker::RangeConstraint::applyAsOutOfRange( 343 ProgramStateRef State, const CallEvent &Call, 344 const Summary &Summary) const { 345 346 ProgramStateManager &Mgr = State->getStateManager(); 347 SValBuilder &SVB = Mgr.getSValBuilder(); 348 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 349 ConstraintManager &CM = Mgr.getConstraintManager(); 350 QualType T = getArgType(Summary, getArgNo()); 351 SVal V = getArgSVal(Call, getArgNo()); 352 353 if (auto N = V.getAs<NonLoc>()) { 354 const IntRangeVector &R = getRanges(); 355 size_t E = R.size(); 356 for (size_t I = 0; I != E; ++I) { 357 const llvm::APSInt &Min = BVF.getValue(R[I].first, T); 358 const llvm::APSInt &Max = BVF.getValue(R[I].second, T); 359 assert(Min <= Max); 360 State = CM.assumeInclusiveRange(State, *N, Min, Max, false); 361 if (!State) 362 break; 363 } 364 } 365 366 return State; 367 } 368 369 ProgramStateRef StdLibraryFunctionsChecker::RangeConstraint::applyAsWithinRange( 370 ProgramStateRef State, const CallEvent &Call, 371 const Summary &Summary) const { 372 373 ProgramStateManager &Mgr = State->getStateManager(); 374 SValBuilder &SVB = Mgr.getSValBuilder(); 375 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 376 ConstraintManager &CM = Mgr.getConstraintManager(); 377 QualType T = getArgType(Summary, getArgNo()); 378 SVal V = getArgSVal(Call, getArgNo()); 379 380 // "WithinRange R" is treated as "outside [T_MIN, T_MAX] \ R". 381 // We cut off [T_MIN, min(R) - 1] and [max(R) + 1, T_MAX] if necessary, 382 // and then cut away all holes in R one by one. 383 // 384 // E.g. consider a range list R as [A, B] and [C, D] 385 // -------+--------+------------------+------------+-----------> 386 // A B C D 387 // Then we assume that the value is not in [-inf, A - 1], 388 // then not in [D + 1, +inf], then not in [B + 1, C - 1] 389 if (auto N = V.getAs<NonLoc>()) { 390 const IntRangeVector &R = getRanges(); 391 size_t E = R.size(); 392 393 const llvm::APSInt &MinusInf = BVF.getMinValue(T); 394 const llvm::APSInt &PlusInf = BVF.getMaxValue(T); 395 396 const llvm::APSInt &Left = BVF.getValue(R[0].first - 1ULL, T); 397 if (Left != PlusInf) { 398 assert(MinusInf <= Left); 399 State = CM.assumeInclusiveRange(State, *N, MinusInf, Left, false); 400 if (!State) 401 return nullptr; 402 } 403 404 const llvm::APSInt &Right = BVF.getValue(R[E - 1].second + 1ULL, T); 405 if (Right != MinusInf) { 406 assert(Right <= PlusInf); 407 State = CM.assumeInclusiveRange(State, *N, Right, PlusInf, false); 408 if (!State) 409 return nullptr; 410 } 411 412 for (size_t I = 1; I != E; ++I) { 413 const llvm::APSInt &Min = BVF.getValue(R[I - 1].second + 1ULL, T); 414 const llvm::APSInt &Max = BVF.getValue(R[I].first - 1ULL, T); 415 if (Min <= Max) { 416 State = CM.assumeInclusiveRange(State, *N, Min, Max, false); 417 if (!State) 418 return nullptr; 419 } 420 } 421 } 422 423 return State; 424 } 425 426 ProgramStateRef StdLibraryFunctionsChecker::ComparisonConstraint::apply( 427 ProgramStateRef State, const CallEvent &Call, 428 const Summary &Summary) const { 429 430 ProgramStateManager &Mgr = State->getStateManager(); 431 SValBuilder &SVB = Mgr.getSValBuilder(); 432 QualType CondT = SVB.getConditionType(); 433 QualType T = getArgType(Summary, getArgNo()); 434 SVal V = getArgSVal(Call, getArgNo()); 435 436 BinaryOperator::Opcode Op = getOpcode(); 437 ArgNo OtherArg = getOtherArgNo(); 438 SVal OtherV = getArgSVal(Call, OtherArg); 439 QualType OtherT = getArgType(Call, OtherArg); 440 // Note: we avoid integral promotion for comparison. 441 OtherV = SVB.evalCast(OtherV, T, OtherT); 442 if (auto CompV = SVB.evalBinOp(State, Op, V, OtherV, CondT) 443 .getAs<DefinedOrUnknownSVal>()) 444 State = State->assume(*CompV, true); 445 return State; 446 } 447 448 void StdLibraryFunctionsChecker::checkPreCall(const CallEvent &Call, 449 CheckerContext &C) const { 450 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 451 if (!FoundSummary) 452 return; 453 454 const Summary &Summary = *FoundSummary; 455 ProgramStateRef State = C.getState(); 456 457 for (const ValueConstraintPtr& VC : Summary.ArgConstraints) { 458 ProgramStateRef SuccessSt = VC->apply(State, Call, Summary); 459 ProgramStateRef FailureSt = VC->negate()->apply(State, Call, Summary); 460 // The argument constraint is not satisfied. 461 if (FailureSt && !SuccessSt) { 462 if (ExplodedNode *N = C.generateErrorNode(State)) 463 reportBug(Call, N, C); 464 break; 465 } else { 466 // Apply the constraint even if we cannot reason about the argument. This 467 // means both SuccessSt and FailureSt can be true. If we weren't applying 468 // the constraint that would mean that symbolic execution continues on a 469 // code whose behaviour is undefined. 470 assert(SuccessSt); 471 C.addTransition(SuccessSt); 472 } 473 } 474 } 475 476 void StdLibraryFunctionsChecker::checkPostCall(const CallEvent &Call, 477 CheckerContext &C) const { 478 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 479 if (!FoundSummary) 480 return; 481 482 // Now apply the constraints. 483 const Summary &Summary = *FoundSummary; 484 ProgramStateRef State = C.getState(); 485 486 // Apply case/branch specifications. 487 for (const auto &VRS : Summary.CaseConstraints) { 488 ProgramStateRef NewState = State; 489 for (const auto &VR: VRS) { 490 NewState = VR->apply(NewState, Call, Summary); 491 if (!NewState) 492 break; 493 } 494 495 if (NewState && NewState != State) 496 C.addTransition(NewState); 497 } 498 } 499 500 bool StdLibraryFunctionsChecker::evalCall(const CallEvent &Call, 501 CheckerContext &C) const { 502 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 503 if (!FoundSummary) 504 return false; 505 506 const Summary &Summary = *FoundSummary; 507 switch (Summary.InvalidationKd) { 508 case EvalCallAsPure: { 509 ProgramStateRef State = C.getState(); 510 const LocationContext *LC = C.getLocationContext(); 511 const auto *CE = cast_or_null<CallExpr>(Call.getOriginExpr()); 512 SVal V = C.getSValBuilder().conjureSymbolVal( 513 CE, LC, CE->getType().getCanonicalType(), C.blockCount()); 514 State = State->BindExpr(CE, LC, V); 515 C.addTransition(State); 516 return true; 517 } 518 case NoEvalCall: 519 // Summary tells us to avoid performing eval::Call. The function is possibly 520 // evaluated by another checker, or evaluated conservatively. 521 return false; 522 } 523 llvm_unreachable("Unknown invalidation kind!"); 524 } 525 526 bool StdLibraryFunctionsChecker::Summary::matchesCall( 527 const CallExpr *CE) const { 528 // Check number of arguments: 529 if (CE->getNumArgs() != ArgTys.size()) 530 return false; 531 532 // Check return type if relevant: 533 if (!RetTy.isNull() && RetTy != CE->getType().getCanonicalType()) 534 return false; 535 536 // Check argument types when relevant: 537 for (size_t I = 0, E = ArgTys.size(); I != E; ++I) { 538 QualType FormalT = ArgTys[I]; 539 // Null type marks irrelevant arguments. 540 if (FormalT.isNull()) 541 continue; 542 543 assertTypeSuitableForSummary(FormalT); 544 545 QualType ActualT = StdLibraryFunctionsChecker::getArgType(CE, I); 546 assert(ActualT.isCanonical()); 547 if (ActualT != FormalT) 548 return false; 549 } 550 551 return true; 552 } 553 554 Optional<StdLibraryFunctionsChecker::Summary> 555 StdLibraryFunctionsChecker::findFunctionSummary(const FunctionDecl *FD, 556 const CallExpr *CE, 557 CheckerContext &C) const { 558 // Note: we cannot always obtain FD from CE 559 // (eg. virtual call, or call by pointer). 560 assert(CE); 561 562 if (!FD) 563 return None; 564 565 initFunctionSummaries(C); 566 567 IdentifierInfo *II = FD->getIdentifier(); 568 if (!II) 569 return None; 570 StringRef Name = II->getName(); 571 if (Name.empty() || !C.isCLibraryFunction(FD, Name)) 572 return None; 573 574 auto FSMI = FunctionSummaryMap.find(Name); 575 if (FSMI == FunctionSummaryMap.end()) 576 return None; 577 578 // Verify that function signature matches the spec in advance. 579 // Otherwise we might be modeling the wrong function. 580 // Strict checking is important because we will be conducting 581 // very integral-type-sensitive operations on arguments and 582 // return values. 583 const Summaries &SpecVariants = FSMI->second; 584 for (const Summary &Spec : SpecVariants) 585 if (Spec.matchesCall(CE)) 586 return Spec; 587 588 return None; 589 } 590 591 Optional<StdLibraryFunctionsChecker::Summary> 592 StdLibraryFunctionsChecker::findFunctionSummary(const CallEvent &Call, 593 CheckerContext &C) const { 594 const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(Call.getDecl()); 595 if (!FD) 596 return None; 597 const CallExpr *CE = dyn_cast_or_null<CallExpr>(Call.getOriginExpr()); 598 if (!CE) 599 return None; 600 return findFunctionSummary(FD, CE, C); 601 } 602 603 void StdLibraryFunctionsChecker::initFunctionSummaries( 604 CheckerContext &C) const { 605 if (!FunctionSummaryMap.empty()) 606 return; 607 608 SValBuilder &SVB = C.getSValBuilder(); 609 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 610 const ASTContext &ACtx = BVF.getContext(); 611 612 // These types are useful for writing specifications quickly, 613 // New specifications should probably introduce more types. 614 // Some types are hard to obtain from the AST, eg. "ssize_t". 615 // In such cases it should be possible to provide multiple variants 616 // of function summary for common cases (eg. ssize_t could be int or long 617 // or long long, so three summary variants would be enough). 618 // Of course, function variants are also useful for C++ overloads. 619 const QualType 620 Irrelevant{}; // A placeholder, whenever we do not care about the type. 621 const QualType IntTy = ACtx.IntTy; 622 const QualType LongTy = ACtx.LongTy; 623 const QualType LongLongTy = ACtx.LongLongTy; 624 const QualType SizeTy = ACtx.getSizeType(); 625 const QualType VoidPtrTy = ACtx.VoidPtrTy; // void *T 626 const QualType ConstVoidPtrTy = 627 ACtx.getPointerType(ACtx.VoidTy.withConst()); // const void *T 628 629 const RangeInt IntMax = BVF.getMaxValue(IntTy).getLimitedValue(); 630 const RangeInt LongMax = BVF.getMaxValue(LongTy).getLimitedValue(); 631 const RangeInt LongLongMax = BVF.getMaxValue(LongLongTy).getLimitedValue(); 632 633 // Set UCharRangeMax to min of int or uchar maximum value. 634 // The C standard states that the arguments of functions like isalpha must 635 // be representable as an unsigned char. Their type is 'int', so the max 636 // value of the argument should be min(UCharMax, IntMax). This just happen 637 // to be true for commonly used and well tested instruction set 638 // architectures, but not for others. 639 const RangeInt UCharRangeMax = 640 std::min(BVF.getMaxValue(ACtx.UnsignedCharTy).getLimitedValue(), IntMax); 641 642 // The platform dependent value of EOF. 643 // Try our best to parse this from the Preprocessor, otherwise fallback to -1. 644 const auto EOFv = [&C]() -> RangeInt { 645 if (const llvm::Optional<int> OptInt = 646 tryExpandAsInteger("EOF", C.getPreprocessor())) 647 return *OptInt; 648 return -1; 649 }(); 650 651 // We are finally ready to define specifications for all supported functions. 652 // 653 // The signature needs to have the correct number of arguments. 654 // However, we insert `Irrelevant' when the type is insignificant. 655 // 656 // Argument ranges should always cover all variants. If return value 657 // is completely unknown, omit it from the respective range set. 658 // 659 // All types in the spec need to be canonical. 660 // 661 // Every item in the list of range sets represents a particular 662 // execution path the analyzer would need to explore once 663 // the call is modeled - a new program state is constructed 664 // for every range set, and each range line in the range set 665 // corresponds to a specific constraint within this state. 666 // 667 // Upon comparing to another argument, the other argument is casted 668 // to the current argument's type. This avoids proper promotion but 669 // seems useful. For example, read() receives size_t argument, 670 // and its return value, which is of type ssize_t, cannot be greater 671 // than this argument. If we made a promotion, and the size argument 672 // is equal to, say, 10, then we'd impose a range of [0, 10] on the 673 // return value, however the correct range is [-1, 10]. 674 // 675 // Please update the list of functions in the header after editing! 676 // 677 678 // Below are helpers functions to create the summaries. 679 auto ArgumentCondition = [](ArgNo ArgN, RangeKind Kind, 680 IntRangeVector Ranges) { 681 return std::make_shared<RangeConstraint>(ArgN, Kind, Ranges); 682 }; 683 struct { 684 auto operator()(RangeKind Kind, IntRangeVector Ranges) { 685 return std::make_shared<RangeConstraint>(Ret, Kind, Ranges); 686 } 687 auto operator()(BinaryOperator::Opcode Op, ArgNo OtherArgN) { 688 return std::make_shared<ComparisonConstraint>(Ret, Op, OtherArgN); 689 } 690 } ReturnValueCondition; 691 auto Range = [](RangeInt b, RangeInt e) { 692 return IntRangeVector{std::pair<RangeInt, RangeInt>{b, e}}; 693 }; 694 auto SingleValue = [](RangeInt v) { 695 return IntRangeVector{std::pair<RangeInt, RangeInt>{v, v}}; 696 }; 697 auto LessThanOrEq = BO_LE; 698 auto NotNull = [&](ArgNo ArgN) { 699 return std::make_shared<NotNullConstraint>(ArgN); 700 }; 701 702 using RetType = QualType; 703 // Templates for summaries that are reused by many functions. 704 auto Getc = [&]() { 705 return Summary(ArgTypes{Irrelevant}, RetType{IntTy}, NoEvalCall) 706 .Case({ReturnValueCondition(WithinRange, 707 {{EOFv, EOFv}, {0, UCharRangeMax}})}); 708 }; 709 auto Read = [&](RetType R, RangeInt Max) { 710 return Summary(ArgTypes{Irrelevant, Irrelevant, SizeTy}, RetType{R}, 711 NoEvalCall) 712 .Case({ReturnValueCondition(LessThanOrEq, ArgNo(2)), 713 ReturnValueCondition(WithinRange, Range(-1, Max))}); 714 }; 715 auto Fread = [&]() { 716 return Summary(ArgTypes{VoidPtrTy, Irrelevant, SizeTy, Irrelevant}, 717 RetType{SizeTy}, NoEvalCall) 718 .Case({ 719 ReturnValueCondition(LessThanOrEq, ArgNo(2)), 720 }) 721 .ArgConstraint(NotNull(ArgNo(0))); 722 }; 723 auto Fwrite = [&]() { 724 return Summary(ArgTypes{ConstVoidPtrTy, Irrelevant, SizeTy, Irrelevant}, 725 RetType{SizeTy}, NoEvalCall) 726 .Case({ 727 ReturnValueCondition(LessThanOrEq, ArgNo(2)), 728 }) 729 .ArgConstraint(NotNull(ArgNo(0))); 730 }; 731 auto Getline = [&](RetType R, RangeInt Max) { 732 return Summary(ArgTypes{Irrelevant, Irrelevant, Irrelevant}, RetType{R}, 733 NoEvalCall) 734 .Case({ReturnValueCondition(WithinRange, {{-1, -1}, {1, Max}})}); 735 }; 736 737 FunctionSummaryMap = { 738 // The isascii() family of functions. 739 // The behavior is undefined if the value of the argument is not 740 // representable as unsigned char or is not equal to EOF. See e.g. C99 741 // 7.4.1.2 The isalpha function (p: 181-182). 742 { 743 "isalnum", 744 Summaries{ 745 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 746 // Boils down to isupper() or islower() or isdigit(). 747 .Case( 748 {ArgumentCondition(0U, WithinRange, 749 {{'0', '9'}, {'A', 'Z'}, {'a', 'z'}}), 750 ReturnValueCondition(OutOfRange, SingleValue(0))}) 751 // The locale-specific range. 752 // No post-condition. We are completely unaware of 753 // locale-specific return values. 754 .Case({ArgumentCondition(0U, WithinRange, 755 {{128, UCharRangeMax}})}) 756 .Case({ArgumentCondition(0U, OutOfRange, 757 {{'0', '9'}, 758 {'A', 'Z'}, 759 {'a', 'z'}, 760 {128, UCharRangeMax}}), 761 ReturnValueCondition(WithinRange, SingleValue(0))}) 762 .ArgConstraint(ArgumentCondition( 763 0U, WithinRange, {{EOFv, EOFv}, {0, UCharRangeMax}}))}, 764 }, 765 { 766 "isalpha", 767 Summaries{ 768 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 769 .Case({ArgumentCondition(0U, WithinRange, 770 {{'A', 'Z'}, {'a', 'z'}}), 771 ReturnValueCondition(OutOfRange, SingleValue(0))}) 772 // The locale-specific range. 773 .Case({ArgumentCondition(0U, WithinRange, 774 {{128, UCharRangeMax}})}) 775 .Case({ArgumentCondition( 776 0U, OutOfRange, 777 {{'A', 'Z'}, {'a', 'z'}, {128, UCharRangeMax}}), 778 ReturnValueCondition(WithinRange, SingleValue(0))})}, 779 }, 780 { 781 "isascii", 782 Summaries{ 783 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 784 .Case({ArgumentCondition(0U, WithinRange, Range(0, 127)), 785 ReturnValueCondition(OutOfRange, SingleValue(0))}) 786 .Case({ArgumentCondition(0U, OutOfRange, Range(0, 127)), 787 ReturnValueCondition(WithinRange, SingleValue(0))})}, 788 }, 789 { 790 "isblank", 791 Summaries{ 792 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 793 .Case({ArgumentCondition(0U, WithinRange, 794 {{'\t', '\t'}, {' ', ' '}}), 795 ReturnValueCondition(OutOfRange, SingleValue(0))}) 796 .Case({ArgumentCondition(0U, OutOfRange, 797 {{'\t', '\t'}, {' ', ' '}}), 798 ReturnValueCondition(WithinRange, SingleValue(0))})}, 799 }, 800 { 801 "iscntrl", 802 Summaries{ 803 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 804 .Case({ArgumentCondition(0U, WithinRange, 805 {{0, 32}, {127, 127}}), 806 ReturnValueCondition(OutOfRange, SingleValue(0))}) 807 .Case( 808 {ArgumentCondition(0U, OutOfRange, {{0, 32}, {127, 127}}), 809 ReturnValueCondition(WithinRange, SingleValue(0))})}, 810 }, 811 { 812 "isdigit", 813 Summaries{ 814 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 815 .Case({ArgumentCondition(0U, WithinRange, Range('0', '9')), 816 ReturnValueCondition(OutOfRange, SingleValue(0))}) 817 .Case({ArgumentCondition(0U, OutOfRange, Range('0', '9')), 818 ReturnValueCondition(WithinRange, SingleValue(0))})}, 819 }, 820 { 821 "isgraph", 822 Summaries{ 823 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 824 .Case({ArgumentCondition(0U, WithinRange, Range(33, 126)), 825 ReturnValueCondition(OutOfRange, SingleValue(0))}) 826 .Case({ArgumentCondition(0U, OutOfRange, Range(33, 126)), 827 ReturnValueCondition(WithinRange, SingleValue(0))})}, 828 }, 829 { 830 "islower", 831 Summaries{ 832 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 833 // Is certainly lowercase. 834 .Case({ArgumentCondition(0U, WithinRange, Range('a', 'z')), 835 ReturnValueCondition(OutOfRange, SingleValue(0))}) 836 // Is ascii but not lowercase. 837 .Case({ArgumentCondition(0U, WithinRange, Range(0, 127)), 838 ArgumentCondition(0U, OutOfRange, Range('a', 'z')), 839 ReturnValueCondition(WithinRange, SingleValue(0))}) 840 // The locale-specific range. 841 .Case({ArgumentCondition(0U, WithinRange, 842 {{128, UCharRangeMax}})}) 843 // Is not an unsigned char. 844 .Case({ArgumentCondition(0U, OutOfRange, 845 Range(0, UCharRangeMax)), 846 ReturnValueCondition(WithinRange, SingleValue(0))})}, 847 }, 848 { 849 "isprint", 850 Summaries{ 851 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 852 .Case({ArgumentCondition(0U, WithinRange, Range(32, 126)), 853 ReturnValueCondition(OutOfRange, SingleValue(0))}) 854 .Case({ArgumentCondition(0U, OutOfRange, Range(32, 126)), 855 ReturnValueCondition(WithinRange, SingleValue(0))})}, 856 }, 857 { 858 "ispunct", 859 Summaries{ 860 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 861 .Case({ArgumentCondition( 862 0U, WithinRange, 863 {{'!', '/'}, {':', '@'}, {'[', '`'}, {'{', '~'}}), 864 ReturnValueCondition(OutOfRange, SingleValue(0))}) 865 .Case({ArgumentCondition( 866 0U, OutOfRange, 867 {{'!', '/'}, {':', '@'}, {'[', '`'}, {'{', '~'}}), 868 ReturnValueCondition(WithinRange, SingleValue(0))})}, 869 }, 870 { 871 "isspace", 872 Summaries{ 873 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 874 // Space, '\f', '\n', '\r', '\t', '\v'. 875 .Case({ArgumentCondition(0U, WithinRange, 876 {{9, 13}, {' ', ' '}}), 877 ReturnValueCondition(OutOfRange, SingleValue(0))}) 878 // The locale-specific range. 879 .Case({ArgumentCondition(0U, WithinRange, 880 {{128, UCharRangeMax}})}) 881 .Case({ArgumentCondition( 882 0U, OutOfRange, 883 {{9, 13}, {' ', ' '}, {128, UCharRangeMax}}), 884 ReturnValueCondition(WithinRange, SingleValue(0))})}, 885 }, 886 { 887 "isupper", 888 Summaries{ 889 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 890 // Is certainly uppercase. 891 .Case({ArgumentCondition(0U, WithinRange, Range('A', 'Z')), 892 ReturnValueCondition(OutOfRange, SingleValue(0))}) 893 // The locale-specific range. 894 .Case({ArgumentCondition(0U, WithinRange, 895 {{128, UCharRangeMax}})}) 896 // Other. 897 .Case({ArgumentCondition(0U, OutOfRange, 898 {{'A', 'Z'}, {128, UCharRangeMax}}), 899 ReturnValueCondition(WithinRange, SingleValue(0))})}, 900 }, 901 { 902 "isxdigit", 903 Summaries{ 904 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 905 .Case( 906 {ArgumentCondition(0U, WithinRange, 907 {{'0', '9'}, {'A', 'F'}, {'a', 'f'}}), 908 ReturnValueCondition(OutOfRange, SingleValue(0))}) 909 .Case( 910 {ArgumentCondition(0U, OutOfRange, 911 {{'0', '9'}, {'A', 'F'}, {'a', 'f'}}), 912 ReturnValueCondition(WithinRange, SingleValue(0))})}, 913 }, 914 915 // The getc() family of functions that returns either a char or an EOF. 916 {"getc", Summaries{Getc()}}, 917 {"fgetc", Summaries{Getc()}}, 918 {"getchar", 919 Summaries{Summary(ArgTypes{}, RetType{IntTy}, NoEvalCall) 920 .Case({ReturnValueCondition( 921 WithinRange, {{EOFv, EOFv}, {0, UCharRangeMax}})})}}, 922 923 // read()-like functions that never return more than buffer size. 924 // We are not sure how ssize_t is defined on every platform, so we 925 // provide three variants that should cover common cases. 926 {"read", Summaries{Read(IntTy, IntMax), Read(LongTy, LongMax), 927 Read(LongLongTy, LongLongMax)}}, 928 {"write", Summaries{Read(IntTy, IntMax), Read(LongTy, LongMax), 929 Read(LongLongTy, LongLongMax)}}, 930 {"fread", Summaries{Fread()}}, 931 {"fwrite", Summaries{Fwrite()}}, 932 // getline()-like functions either fail or read at least the delimiter. 933 {"getline", Summaries{Getline(IntTy, IntMax), Getline(LongTy, LongMax), 934 Getline(LongLongTy, LongLongMax)}}, 935 {"getdelim", Summaries{Getline(IntTy, IntMax), Getline(LongTy, LongMax), 936 Getline(LongLongTy, LongLongMax)}}, 937 }; 938 } 939 940 void ento::registerStdCLibraryFunctionsChecker(CheckerManager &mgr) { 941 mgr.registerChecker<StdLibraryFunctionsChecker>(); 942 } 943 944 bool ento::shouldRegisterStdCLibraryFunctionsChecker(const LangOptions &LO) { 945 return true; 946 } 947 948 #define REGISTER_CHECKER(name) \ 949 void ento::register##name(CheckerManager &mgr) { \ 950 StdLibraryFunctionsChecker *checker = \ 951 mgr.getChecker<StdLibraryFunctionsChecker>(); \ 952 checker->ChecksEnabled[StdLibraryFunctionsChecker::CK_##name] = true; \ 953 checker->CheckNames[StdLibraryFunctionsChecker::CK_##name] = \ 954 mgr.getCurrentCheckerName(); \ 955 } \ 956 \ 957 bool ento::shouldRegister##name(const LangOptions &LO) { return true; } 958 959 REGISTER_CHECKER(StdCLibraryFunctionArgsChecker) 960